Butterfly is the most demanding swimming stroke, but its core mechanic is simpler than it looks: a wave that travels from your chest through your hips and out through your feet, combined with a simultaneous arm pull. Every part of the stroke serves that wave. Once you understand the body undulation, the arms and kicks layer on top naturally.
The Body Wave Comes First
Before thinking about arms or kicks, you need to feel the undulation. Press your chest down into the water, then release it. That press-and-release travels down your torso like a whip, reaching your hips and then your feet with increasing speed. Researchers describe this as a “whip-like action” where forward motion transfers through each body segment in sequence. The wave starts small at your chest and amplifies by the time it reaches your legs.
A common mistake is trying to generate all the movement from your hips or knees. The wave genuinely begins at the chest. Think of it as rocking your ribcage: when your chest presses down, your hips rise slightly. When your chest rises, your hips drop. Your knees bend only as a consequence of that wave reaching your legs, not because you’re actively kicking from the knee. Practice this motion on its own, face down in the water with your arms at your sides, before adding anything else.
Two Kicks Per Stroke Cycle
Each full butterfly cycle includes two dolphin kicks, and their timing relative to your arms is what makes the stroke feel rhythmic rather than chaotic.
The first kick is the bigger one. Its downbeat happens as your hands enter the water in front of your shoulders and stretch forward. This kick drives your body into the streamlined, stretched position at the front of the stroke. Think of it as “kicking your hands into the water.”
The second kick is smaller. Its downbeat occurs as your arms sweep back past your chest toward your hips, during the power phase of the pull. This kick helps lift your upper body and shoulders so your arms can exit the water for the recovery. Think of it as “kicking your hands out of the water.”
Between downbeats, your legs naturally rise back toward the surface. You don’t need to think much about the upbeat. Focus on snapping the downbeats at those two moments: hands entering, then hands exiting.
The Arm Pull: Three Sweeps
Your arms enter the water about shoulder width apart, led by the thumbs, with your elbows slightly higher than your hands. From there, the pull breaks into three connected sweeps.
- Outsweep: Your hands press down and out, forming a Y shape in front of your body. This is the “catch,” where you find your grip on the water.
- Insweep: Turn your hands back in toward each other, keeping your elbows high and wide. Your hands pass under your chest. This is where real propulsion begins, powered primarily by the large muscles of your chest and back.
- Upsweep: Your hands turn outward again and push back along your sides toward your hips. This is the final acceleration before your arms leave the water.
The path your hands trace underwater roughly resembles a keyhole shape: wide at the top, narrow in the middle, then pushing back. After the upsweep, your arms exit the water near your hips and swing forward just above the surface for the recovery. Keep the recovery low. Most wasted energy in butterfly comes from moving your body up and down rather than forward, so swinging your arms high overhead is counterproductive. Skim them just over the water’s surface.
When and How to Breathe
Breathing in butterfly is built into the stroke’s natural rhythm. As your arms pull through the insweep and upsweep, your shoulders and upper body rise. That’s your window. Start lifting your chin forward (not up) as you begin applying pressure during the pull. By the time your hands reach your hips, your mouth clears the surface for a quick inhale.
The critical part is getting your head back down before your arms re-enter the water. Your face should be back in the water, looking slightly forward and down, before your hands touch the surface. If your head is still up when your arms enter, you lose the streamlined body position and the first kick can’t do its job. A useful cue from U.S. Masters Swimming: breathe with your pull, and get your head down ahead of your recovery. Breathe as your body rises, lower your head as your body falls.
Keep your head low when you breathe. You only need your mouth to clear the surface, not your entire face. Some swimmers breathe every stroke, others every other stroke. Every other stroke is easier on your timing while you’re learning, but either pattern works once the rhythm is solid.
Protecting Your Shoulders
Butterfly puts significant demand on the shoulder joint, and one specific technique error increases your injury risk: entering the water with your hands too wide. Research on swimmers with painful shoulders found that a wider hand entry changes how the shoulder blade sits, rotating it downward and reducing the space where the rotator cuff tendons pass. This leads to impingement, where those tendons get pinched with every stroke.
The fix is straightforward. Enter with your hands no wider than shoulder width, thumbs first, elbows slightly bent. If you notice shoulder pain during or after butterfly sets, check your entry width first. Strengthening the muscles that stabilize your shoulder blade (the ones between your shoulder blades and along the side of your ribcage) also helps maintain healthy positioning throughout the stroke.
Drills to Build the Stroke
Trying to swim full butterfly on your first attempt usually leads to frustration. These drills build the pieces in order.
Body dolphin. Push off the wall face down, arms at your sides or extended in front, and practice the undulation at the surface. Focus on initiating from your chest. Do this until the wave feels easy and continuous, not choppy.
Three kicks, one pull. Swim with three dolphin kicks between each arm pull. This slows the stroke down dramatically and gives you time to feel the connection between the kick and the pull without rushing. It also builds kick endurance.
Breathe, pull, glide. Take one breath, execute one full arm pull with two kicks, then glide in the streamlined position before starting the next cycle. This drill teaches you to find the glide at the front of each stroke rather than churning through without pause.
Three left, three right, three full (333). Swim three strokes pulling with your left arm only (right arm extended), three with your right arm only, then three full butterfly strokes. This builds rhythm and helps each arm develop equal strength and timing. Single-arm butterfly is also much less tiring, so you can focus on technique without gasping.
Putting the Timing Together
The full stroke cycle, from the swimmer’s perspective, feels like this: your hands enter the water as you snap the first kick down, and your body stretches long. Your hands catch the water and begin the outsweep and insweep as your legs rise. As your hands push back past your hips and your arms start to exit, the second kick snaps down, your chest rises, and you take a breath if you need one. Your arms swing low over the surface, your face drops back into the water, and the cycle restarts with the next entry and first kick.
The rhythm has a distinct “da-DUM” feel: a smaller second kick followed by the bigger first kick, repeating continuously. Many coaches describe it as a galloping rhythm rather than an even beat. When the timing clicks, butterfly shifts from exhausting to surprisingly sustainable. You’re riding the wave your body creates rather than fighting the water with brute force.
Butterfly does burn energy faster than any other stroke, roughly 800 or more calories per hour compared to about 600 for freestyle and 500 for backstroke. But much of that cost drops when technique improves. Efficient butterfliers look almost relaxed because they minimize vertical movement and let the undulation do the work. If you feel like you’re wrestling the water, slow down, return to the drills, and focus on the wave.